How Environmental Noise Harms the Cardiovascular System
Prior to Covid-19, a slew of research internationally revealed an increasingly noisy world. While this changed significantly during periods of pandemic lockdowns in
major cities (https://www.sonitussystems.com/news/least-human-made-noise-pollution-in-recorded-history), as businesses start to reopen and something resembling normal life resumes, so too will noise.
While unwanted noise such as that of transportation and industrial operations is more commonly perceived as a nuisance, it has the potential to cause serious physical harm to the human body and mind.
In an article for The-Scientist.com, researchers for the Department of Cardiology at
the University Medical Center of the Johannes Gutenberg University, Thomas Münzel and Omar Hahad, detail the harm that noise is having on our cardiovascular system.
The detrimental effects of noise have been known for over a century, with the German physician Robert Koch observing sleep disturbances, increased anger, tinnitus, and coronary heart disease. Research
on noise has intensified ever since the World Health Organization concluded that people lose up to 1.6 million years of healthy life in Western Europe alone due to transportation-related noise. Similarly,
in 2015, an EEA study linked such excessive noise to 1.7 million cases of hypertension, 80,000 hospital admissions, and 18,000 premature deaths.
In their current research, which is the subject of the above-mentioned article, Münzel and Hahad seek to discover the effects noise pollution has on the cardiovascular system.
Over the years, the non-auditory harm that noise can cause has been explored by various researchers. Karl Kryter, working for the Air Force's Air Research and Development Command in 1950, first
proposed this 'indirect harm', proposing noise stimulates neural systems such as the autonomic nervous system. Furthering our understanding in 1968, Gerd Jansen from the Max Plack Institute examined
1,005 industrial workers exposed to a continually noisy environment. He observed this chronic noise exposure led to circulation issues as well as balance and heart problems.
More recently, in 2003, Wolfgang Babisch devised the noise reaction model to determine the adverse effects of noise on our health. The model describes two "pathways" of noise-related harm. The first is
direct exposure to overly loud noise, over 90 decibels. The second is indirect, non-auditory exposure to low-level noise around 50-60 decibels. Babisch posited that this second, indirect pathway led to
cardiovascular issues through an increase of stress hormones, high blood pressure, and an elevated heart rate.
Conducting their own research in 2013, Münzel and Omar had participants exposed to recorded aircraft noise overnight. Testing the participant's blood, endothelial function and using questionnaires
concluded that just one night of exposure to aircraft noise led to decreased sleep quality, stiffened blood vessels, and vascular endothelial dysfunction. The researchers claim, aside from these being
symptomatic of atherosclerosis, repeat exposure exacerbated the effects with endothelial functioning worsening when the aircraft noise frequency was doubled.
The mechanisms behind cardiovascular disease and noise are not well explored, with only a few studies attempting to form a link. Babisch proposes that our annoyance reactions lead to cardiovascular
problems, not the noise itself. Some studies, such as one conducted in 2019, indicated increased amygdala activity, related to emotional responses, may be linked to cardiovascular problems. In other words,
it's not the noise, it is our annoyance at the noise that increases stress levels. Either way, the evidence shows noise pollution results in endothelial dysfunction and cardiovascular issues.
Disruption of Limbic System
Another area researchers are currently looking at is the impact noise has on the brain's limbic system, which is a key player in emotional regulation, the sympathetic nervous system, and the release
of stress hormones. It is thought these bodily responses of vascular inflammation, oxidative stress, and altered gene expression may lead to cardiovascular disease.
Münzel and Omar detail the effect as follows:
- Noise-disrupted sleep causes emotional responses via the amygdala.
- It also activates the endocrine and autonomic nervous systems, releasing stress hormones.
- This stress causes physiological risks for cardiovascular disease, including high cholesterol.
- Continued stress leads to an endothelial build-up of this plaque.
- Noise can cause this to rupture, causing cardiovascular disease.
Increased ROS Production
In their studies, Münzel and Omar found that vitamin C lessened the effect of nighttime noise on endothelial function, linking it to its anti-oxidative properties. After studies on mice,
they discovered chronic-noise exposure led to the increased production of reactive oxygen species (ROS) inside vascular lining. In further studies, Münzel and Omar found this oxidative stress
to also be present in the brain of mice, leading to neuroinflammation in the frontal region, perhaps explaining impaired cognition in noisy environments. Causing this increase in ROS, they claim,
are two radical-forming enzymes, Nox2 and eNOS. Notably, in non-noisy conditions, eNOS produces nitric oxide (NO), known for its anti-atherosclerotic effects. When mice were exposed to noise, the
NO became uncoupled, leading to O2 and a pro-atherosclerotic effect.
The researchers found mice that lacked the Nox2 gene were not deleteriously affected by chronic noise, leading them to confirm oxidative stress as the primary factor in cardiovascular damage by noise.
Interestingly, cardiovascular damage was only found in mice who experienced chronic noise during sleeping hours, fragmenting their sleep. Applying these findings to broader society, Münzel and Omar comment
that doctors cannot solve noise pollution, but instead, this is the purview of governments and politicians. Specifically, they suggest policies should be enacted that follow WHO guidelines, with a
mean upper daytime limit of 45 decibels for aircraft noise, 53 for road traffic, and 54 for railway activity. Nighttime level recommendations are even lower to avoid cardiovascular disease in populations,
with environmental monitoring being highly recommended.
The link between noise pollution and cardiovascular disease is now well established. With Münzel and Omar's work, we now better understand the underlying mechanisms that cause
these health issues and can better tackle the growing noise problem.
Sonitus Systems offers both the hardware and software for a range of environmental parameters on a continual basis, with real-time information available through our Sonitus Cloud dashboard.
For more details on our indoor and outdoor noise and air quality monitoring products and services, please contact the team at https://www.sonitussystems.com/contact-us.